A Catholic Reflection on Nicomachus’ Arithmetic, Book I, Chapter 6
From the stars above to the rhythms of time, from the patterns of leaves to the proportions of the human body—there is a deep and undeniable order woven into all creation. In Chapter 6 of his Arithmetic, Nicomachus of Gerasa contemplates this order and declares its source: number, not merely as a human invention, but as a divine idea—immaterial, eternal, and preexistent in the mind of God.
To Nicomachus, number is not only a tool for measuring things in the world; it is the pattern by which the world itself was made. For Catholics, this insight echoes powerfully. Sacred Scripture and Church teaching affirm that God made all things with wisdom and purpose. Number, when rightly understood, becomes a kind of sacrament of divine reason—a visible echo of the invisible order that governs all.
Let us walk through Nicomachus’ teaching, and consider how this ancient arithmetic leads us to contemplate eternal truths.
The World Was Created According to Number
Nicomachus opens this chapter with a majestic claim: everything in the universe, both in part and as a whole, is ordered according to number, by the mind and foresight of the Creator.
This is not merely poetic language—it is a theological statement. Nicomachus holds that number existed first in the mind of God, and that God used it as the preliminary sketch, or divine plan, according to which all things were made.
This idea finds strong resonance in Catholic teaching. The Catechism of the Catholic Church states, “God created the world according to his wisdom. It is not the product of any necessity whatever. He created it freely out of nothing to manifest and communicate his glory” (CCC 295).
The Book of Wisdom confirms this: “You have arranged all things by measure and number and weight” (Wisdom 11:20). The Fathers of the Church, especially St. Augustine, saw in this passage a key to understanding how the world reflects the mind of God. Creation is not a chaotic burst of force—it is a cosmic liturgy of number and form, carried out by divine wisdom.
Number Is Not Material—It Is Eternal
Nicomachus makes a critical clarification: the number by which God created the world is not material. It is not the number written on a page or carved into a stone. It is immaterial and conceptual, known only to the mind, and especially to the divine Mind.
In other words, the number that gives form to all things is not physical—it is eternal essence. It exists independently of time and space. It is the model by which time and space themselves are shaped.
St. Thomas Aquinas would later describe these as divine ideas, existing eternally in God and serving as the patterns by which creatures are made. Number, in this view, is not a product of human thinking—it is a participation in eternal reason.
And because we, too, are made in the image of God, we can grasp number. Our minds, through reason, are capable of perceiving this immaterial order. This is not mere intellect—it is a form of contemplation. When we study number, we are training our souls to perceive divine wisdom.
Harmony Emerges From Real Opposites in Relation
After establishing the divine origin of number, Nicomachus introduces another profound idea: true harmony arises from the relation of opposites.
He explains that harmony is not made of non-existent things, nor of things that are identical. Rather, it is made of things that are real, different, and related.
This is an ancient philosophical insight with spiritual implications. Harmony requires both contrast and unity. In music, it is the blending of low and high tones. In art, it is the balance of light and dark. In creation, it is the integration of male and female, day and night, body and soul.
St. Augustine, in De Musica, teaches that harmony reflects the unity of the soul and the unity of the cosmos. Everything beautiful, he writes, is beautiful by proportion and relationship.
This insight also reflects a fundamental principle in Christian theology: that truth is often found in the reconciliation of opposites. Christ is both God and man. The Church is both visible and invisible. Grace perfects nature, rather than destroying it. The doctrine of the Trinity teaches three divine Persons in one God. Everywhere in our faith we find unity that does not erase distinction.
So it is with number, says Nicomachus. The first harmony emerges from the union of opposites: odd and even.
Odd and Even: The First Harmony of Number
At the end of this chapter, Nicomachus names the two “most fundamental species” of number: odd and even. These are not merely categories—they are complementary opposites, different but not alien to one another.
Odd and even are both real, and both belong to the same genus: quantity. They differ essentially—an odd number cannot be divided evenly into two whole parts, while an even number can. Yet they are woven together into harmony, he says, “inseparably and uniformly, by a wonderful and divine Nature.”
This divine weaving reflects what we would call in Catholic theology a hierarchical harmony—a unity that respects order and distinction. God does not create by flattening difference, but by ordering it. The harmony of creation reflects this order: day and night, land and sea, man and woman, angel and man, heaven and earth.
Even the Church reflects this harmony. St. Paul writes, “There are different kinds of spiritual gifts but the same Spirit… To each individual the manifestation of the Spirit is given for some benefit” (1 Corinthians 12:4,7). Unity through difference is not only beautiful—it is divine.
Nicomachus sees this same principle in the very structure of number. Before we can speak of ratios or measurements or geometry, we must first perceive the first harmony—the stable joining of odd and even. It is simple, yet wondrous. It is the numerical image of peace.
From Arithmetic to Theology
By now it is clear: for Nicomachus, arithmetic is not about counting. It is about contemplation. Number is the invisible language by which the universe was made. Harmony is the signature of divine authorship. And the union of opposites in number reflects the deeper unity of all creation in the mind of God.
This vision is entirely consistent with Catholic theology. We believe that the visible world reveals the invisible Creator (cf. Romans 1:20). We believe that truth, goodness, and beauty all find their source in the Trinity. And we believe that mathematics, rightly understood, is one of the purest ways to encounter the rationality of creation, which flows from the eternal Word.
St. Thomas Aquinas says, “Beauty consists in due proportion.” When we contemplate the harmony of number, we glimpse the beauty of God.
Conclusion: Number, Harmony, and the Glory of God
Nicomachus reminds us that arithmetic is not small or secondary. It is the first and most profound of the sciences, because it deals not only with quantity but with the very essence of order.
From the harmony of odd and even, to the ratios that govern music, time, and space, we see that creation is structured, measured, and lovingly arranged by a Creator who delights in proportion.
This is why the study of number belongs in the heart of Catholic education—not just as utility, but as formation for contemplation. It is the discipline that teaches the soul to seek unity, to love truth, and to perceive the grandeur of God’s wisdom in the simplest of things.
Let us then, with reverence, look upon number not as man’s invention, but as God’s eternal idea—an idea that brings all things into harmony, and all souls closer to Him.
Mr. William C. Michael, O.P.
Headmaster
Classical Liberal Arts Academy
References
Aristotle. Nicomachean Ethics. Translated by W. D. Ross. https://www.perseus.tufts.edu/hopper/text?doc=Aristot.+Nic.+Eth.
Catechism of the Catholic Church. 2nd ed. Libreria Editrice Vaticana, 1997. https://www.vatican.va/archive/ENG0015/_INDEX.HTM
Holy Bible. New American Bible, Revised Edition (NABRE). United States Conference of Catholic Bishops, 2011. https://bible.usccb.org/
Nicomachus of Gerasa. Introduction to Arithmetic. Translated by Martin L. D’Ooge. https://archive.org/details/NicomachusIntroToArithmetic
Plato. Timaeus. Translated by Benjamin Jowett. https://www.perseus.tufts.edu/hopper/text?doc=Plat.+Tim.
St. Augustine. De Musica. https://www.newadvent.org/fathers/
St. Thomas Aquinas. Summa Theologica. https://www.newadvent.org/summa/
Wisdom 11:20. New American Bible. https://bible.usccb.org/
